1. Field of the Invention
The present invention relates to an optical pickup which is employed for reading or writing information from or on an optical disk including a photomagnetic disk or for other purposes.
2. Description of the Prior Art
An optical pickup known heretofore has a structure wherein a lens holder is joined to a base conveyed in a substantially radial direction of an optical disk by a conveying means or to a member for fixation to the base through springs, and thereby is not only conveyed in the aforesaid direction of conveyance, but is also made displaceable elastically in the direction of the optical axis of a lens and substantially in the aforesaid direction of conveyance perpendicular to this direction, wherein two square-tube-shaped focusing coils are bonded to the lens holder in the direction of conveyance of the base with the lens holder held between, wherein tracking coils are bonded on two opposite surfaces of each focusing coil extending in the direction of conveyance of the base so that the respective central parts of the tracking coils are positioned substantially at the corner parts formed by the surfaces of the focusing coils being in contact with the lens holder and by the surfaces thereof extending in the direction of conveyance of the base, and wherein the center yoke part of a yoke fixed to the base is put in the tube of each focusing coil. When a current is made to flow through the tracking coils in the optical pickup of this structure, not only a force in the tracking direction, i.e. the direction of conveyance of the base, is applied to the lens holder by an electromagnetic force, but also a torque around an axis perpendicular to the tracking direction and the focusing direction is applied thereto due to the unbalance of the distribution of the intensity of a magnetic field in the direction of the optical axis of the lens, i.e. the focusing direction, which causes a problem that a transmission characteristic in the direction of tracks is deteriorated.
As an optical pickup solving the above-stated problem, the present inventor invented previously an optical pickup wherein bonding of the tracking coils to the focusing coils was made in the same way as usual with regard to one tracking coil symmetric with respect to the optical axis of the lens, out of two tracking coils of both focusing coils, while the bonding was made, regarding the other tracking coil, in such a manner that the position thereof was shifted to a corner part spaced apart from the lens holder facing the corner part of the focusing coil to which the one tracking coil is bonded, so that it came in substantially equal contact with two surfaces of the focusing coil forming the corner part.
The result of repeated further considerations and examinations of the optical pickup of the abovedescribed prior solution has revealed that there is such a relation as shown in FIG. 4 between a frequency f of the current flowing through the focusing coils and an amplitude dB of the lens holder and that a peak A appearing on the high frequency side of several kilohertz or above has a strong adverse effect on the focusing performance of the optical pickup.